"Our system indicates that you are attempting to access the Coursera site from an IP address associated with a country currently subject to U.S. economic and trade sanctions. In order for Coursera to comply with U.S. export controls, we cannot allow you access to the site."

Coursera is one of the largest providers of massive open online courses, or MOOCs, and students around the world have devoured its offerings. Students who were affected by the blockage expressed disappointment.

"Did you guys just Block us in #Iran ? "Are there #sanctions on educational material too? "With this act you are only helping hardliners in Iran to impose their ideology and beliefs in the absence of a wide-spread, free, higher-education system. "We were just forming a study group here in Tehran last week to join many other study groups. "It is disappointing. "

Coursera co-founder Andrew Ng told us everyone at the company felt "sadness" at the development, which he said happened because Coursera didn't have a specific license from the Treasury Department's Office of Foreign Assets Control to offer services in Cuba, Iran and Sudan. And, he added, Coursera should know in a few weeks if it will be granted the license necessary to provide services in those countries.

Treasury hasn't "made a specific determination, but we remain cautiously optimistic," he said.

A Treasury Department spokeswoman told us that OFAC has a history "of licensing U.S. academic and educational institutions."

"OFAC, in consultation with the State Department, will continue to consider requests by U.S. persons to engage in activities to provide online courses and certificates of mastery to persons located in or ordinarily resident in sanctioned countries," she wrote in an email.

Indeed, edX, a partnership between Harvard and MIT, is another MOOC provider, and its operations haven't been affected.

In a statement, the company told us:

"EdX began working with OFAC and the U.S. State Department last Spring because of our commitment to provide access to education to edX learners worldwide. EdX received confirmation that we could offer education to students to Syria under a general license and we recently received licenses to offer MOOC education to students in Cuba, Iran and Sudan."

Meanwhile, Coursera noted on its website that it had blocked IP addresses in Cuba, Iran, Sudan and Syria. That's when the State Department notified it that the services provided in Syria "fall under an exception ... which authorizes certain services ... in Syria, particularly as they pertain to increasing access to education." So Coursera lifted the block on Syrian access to its material.

The present restriction on dealing with sanctioned nations isn't preventing Coursera from expanding its overseas operations.

Ng told us that Coursera had signed a partnership with the Carlos Slim Foundation that would make more Spanish-language courses available throughout Latin America.